If you could get decent range at a decent speed with pure electric, they would already have taken over. As a hybrid, there are more pieces and parts to fail.

I wonder what the efficiency would be, maintenance wise as well, to have 2 electric drive motors to replace the diesel and then have two smaller generators on board to provide power to batteries, along with solar to alleviate the need to run them constantly.

Worse, the diesel pretty much matches the effiency of a standard drivetrain but then you convert that mechanical energy to electrical with losses, then convert it to chemical (battery) with more losses, then back to electrical with more losses and finally back to mechanical with more losses. All at higher cost and less capability as the smaller generators won't be able to maintain the same kind of power output.

Plus, I'm really for the thought of how much quieter the boat would be. Under normal circumstances you may only need to run the motors for 30 minutes to an hour a day. This should be able to be done without kicking in the generators. For those times you have to raise the iron sail for a few hours, well then you have to deal with the generatornoise. Which I would imagine may be much quieter than the diesel engines.

If you only want a half hour to get in and out of port before putting up the sails, it's doable today but you will have significantly diminished performance under power and will hurt your resale value.

Keep in mind a 20kw generator is significantly larger and heavier than a 20wk propulsionmotor. At the same time for 30-45' boats, its way over sized for house loads, so will be inefficient.

Take a look at my use cases in my earlier posts and see how your system would address them. If you say, you just don't care if you can maintain speed in emergency conditions, that's an option (there are still the stray people going around with no motor at all), but admit it up front and take the time to understand the consequences.

A mechanical power train is a misery, which ships have not any longer!

The vast majority of ships still have mechanical power trains.
It's mostly cruise ships and other specialty ships that have diesel electric because a typical freighter may make port every week or two but a cruise ship is every day or two. Within reason, freighters don't care if it takes a little longer for tugs to push them into position but cruise ships have a few thousand guests on the railing ready to go, so they

Transmission takes up 40+% of the overall engine room and related costs.
I imagine a diesel powering either an hydraulic transmission, or an electric engine coupled to it directly (not thru batteries)

Hydraulic transmissions have been done. They are noisy, less efficient and leaky (yeah, someone will come on and say they don't leak but I've never seen it happen in real life).

If you do diesel electric and omit the batteries, you have diesel motors of higher HP to account losses and then you just replaced the transmission with the actual generator coils plus the drive motors

Batteries could suffice for say 1h maneuvering...

(Q: when are TESLA batteries made available?)You can buy the power wall now but they are not set up for marine applications and may or may not match voltage requirements...plus it's an expensive option.

thus, shortly said, you still depend on your tank reserve. There is NO MAGIC

i do agree with the last statement. If you aren't willing to significantly sacrifice performance, you won't be going electric.

Just scale things back. I could fit a 20kw silenced water cooled diesel generator on my boat with ease.

This means I would have serious power available.

Agreed, its nowhere near the two Chevy V8 engines but still could get me somewhere.
You could still have house batteries, solar panels and an inverter but it would be just so much simpler to run the generator to power your needs unless you prefer a limited minimalist lifestyle.

Just scale things back. I could fit a 20kw silenced water cooled diesel generator on my boat with ease.

This means I would have serious power available.

Agreed, its nowhere near the two Chevy V8 engines but still could get me somewhere.
You could still have house batteries, solar panels and an inverter but it would be just so much simpler to run the generator to power your needs unless you prefer a limited minimalist lifestyle.

What is your goal here?

On a boat, the typical house loads are several orders of magnitude lower than the power needed for long-distance motoring. If you have a hybrid propulsion system then you still have to carry as much or probably more fuel than you would need for a traditional diesel-engine propulsion. Sure, you have an efficient electric motor, but you still have roughly the same power losses in the diesel generator as you would have in a diesel propulsion engine.

If you have this system, yes, you get a source of power perhaps a little more efficient than they typical diesel engine turning a small alternator, but not by much. And any efficiency gain is drastically overshadowed by the end-to-end efficiency *loss* in the hybrid system.

I just don't see the advantage of hybrid here. Boats are not cars, where we mostly drive stop-and-go, and up-and-down hills, so we can take good advantage of regenerative braking (which recovers the energy that would be lost in frictional braking). Passagemaking boats don't stop to plug-in and recharge every twenty (or 200) miles.

If the use-case is just powering in and out of the slip and sailing 100% of the rest of the time, then just go all-electric with a decent battery bank and use shorepower to recharge. Or use solar to recharge over a few days. Hybrid just adds cost and complexity, with no real gain.

I see this use case, liveaboard on the hook in a limited area, not usually traveling long distances, just a bit of puttering around exploring, say in normal usage motoring a dozen or so hours a week.

The genset's needed anyway for House, so propulsion just means upsizing it.

If the platform's designed for massive solar area from the get go, maybe the diesel's barely used at all **when conditions are good**, but it's there for when you need it.

And that's when the LFP bank needs upsizing too, that, the panels and the hull are the "crazy" expenses, not the incremental cost of different motors.

I power my house loads when on the hook with 300W of solar -- hardly extravagant. I need more electrical power when underway for the nav gear and autopilot. I can cut way back on those loads if necessary.

Your statements are correct but the motor generator principle works for large cruise ships. There certainly are a great number of them.

The goal was to see if the principle of operation could be scaled back to suit boats around 30ft in terms of electric propulsion.

There obviously are negatives with respect to conventional diesel/petrol propulsion as well as for hybrid electric propulsion but there seems to be an increasing interest in the latter.

For the moment my boat engines are in top form but when the time comes to repower, I too will be looking at electric options as two chev engines can max out my credit card at the fuel pump with 20liters to the hour fuelconsumption.
Add this to stern drive maintenance issues and the electric system sounds all the more attractive.

Your statements are correct but the motor generator principle works for large cruise ships. There certainly are a great number of them.

True, but with a cruise ship the use case is substantially different. There are tremendous house loads, compared proportionally to a typical private boat. Also, I understand that in the big ships there are multiple generators that are fired up or shut down as the demand requires. This way they can avoid the inefficiencies that exist when you have a single generator sized for your maximum load, but you spend a lot of time running it lightly loaded. I also don't believe that cruise ships have a significant battery bank. These are all important factors.

I love new technology and I would be thrilled to see some breakthroughs in energy generation and storage that could be appropriately applied to small boats. My problem may be that I'm an engineer. I need to do the math. So far, I've been disappointed.

Your statements are correct but the motor generator principle works for large cruise ships. There certainly are a great number of them.

The goal was to see if the principle of operation could be scaled back to suit boats around 30ft in terms of electric propulsion.

There obviously are negatives with respect to conventional diesel/petrol propulsion as well as for hybrid electric propulsion but there seems to be an increasing interest in the latter.

For the moment my boat engines are in top form but when the time comes to repower, I too will be looking at electric options as two chev engines can max out my credit card at the fuel pump with 20liters to the hour fuel consumption.
Add this to stern drive maintenance issues and the electric system sounds all the more attractive.

No one is saying you can't build a diesel-electric. It's actually pretty simple.

The problem is you haven't clearly defined why you want to switch to diesel-electric. If it's just for fuel consumption, straight diesel will win.

I suspect the flaw in your assumption is you are comparing a 20hp diesel-electric system to a pair of 250hp V8 engines and assuming it's the technology that makes the difference.

It's not the technology it's the HP output.
- The 20hp diesel will never get your boat on plane. The V8 engines will.
- If you are willing to accept not getting on plane a pair of 10hp diesels will match the 20hp diesel-electric system and be far more efficient than the V8 engines.

No one is saying you can't build a diesel-electric. It's actually pretty simple.

The problem is you haven't clearly defined why you want to switch to diesel-electric. If it's just for fuel consumption, straight diesel will win.

I suspect the flaw in your assumption is you are comparing a 20hp diesel-electric system to a pair of 250hp V8 engines and assuming it's the technology that makes the difference.

It's not the technology it's the HP output.
- The 20hp diesel will never get your boat on plane. The V8 engines will.
- If you are willing to accept not getting on plane a pair of 10hp diesels will match the 20hp diesel-electric system and be far more efficient than the V8 engines.

So what are you trying to accomplish with a hybrid system?

True, in boat propulsion the engines run near their optimal rpm for long times, thus you won't see any practical fuel saving. However, a combination of a diesel generator + solar + wind might save diesel compared to a straight setup, especially if assisted by a large battery.

True, in boat propulsion the engines run near their optimal rpm for long times, thus you won't see any practical fuel saving. However, a combination of a diesel generator + solar + wind might save diesel compared to a straight setup, especially if assisted by a large battery.

boat: Lagoon 380' - sailing at 8-10kts
Fuel needed for conventional single diesel engine (more efficient): 2l/h. According to the Yanmar curves, this is around 16kW power at the crankshaft.

While sailing at e.g. 9kts, you generate ~1kW with a pair of Watt&Sea 600 hydro generators, +500W from ~10m2 worth of solar panel covering all available deck space + another ~500W from a large wind generator. = Ideally you charge your battery with 2kW. Removing losses and domestic consumption, let that be 1.6kW, 1/10th of the engine's demand.

Assuming you sail half of the day (12 hours), when sun and wind are both available for power generation, you collected ~20kWh which can ease your power need of the next 12 hours (12*16=192kWh) about 10%. I know it's not the world, but that percentage can go up significantly if the motoring period is reduced thank good winds.

I know, its by far not economic (the full refit incl 2 hydrogenerators, solar, big wind gen, diesel gen, electric engine would cost 20+k$=20+tons of diesel!) but might be interesting for extremely long voyages without a gas station in sight.

Based on the above link, 8 kts is flat out and that's consistent with what I would expect for that boat. Cruise is 7kts. So drop that to 8kts and with a pair of 29hp engines (45kw total) at 8-10kts, you are going to use closer to 6L/hr.

It is often possible to go faster under sail but counting on 9kts for a 12hr run would be the sail of a lifetime conditions. 6.5-7.0kts is a bit more realistic (and still better than average for a 12hr sail). Taking the graph from your link for the hydro generators and following down from 500w @ 9 kt, brings you down to a little over 200w each or 400w total. On a 12hr run, that works out to 4.8kwh.

500w of solar only applies on sunny days when the sun is nearly overhead. Generally it's assumed it averages out to about 4hrs at the rated output, so solar is only going to put out 2kwh per day.

So your 20kwh drops to 6.8kwh. At 45kw for 8kts, that's about 9 minutes of motoring time under very good conditions.

In more moderate sailing conditions say averaging 4kts, the total of solar and hydro drops to around 4.5kwh, or about 6 minutes. of motoring time per day.

It's not that I don't want you to be right. I wish a modest size solar array could put out 20kw for 10hr per day and a 200kwh battery bank to hold that power weighed 100lbs and only cost $200. Of course if that were true, all new boats would be solar powered already.